Carrier-current phase-angle relaying system



A; C. MEHRING ETAL CARRIER-CURRENT PHASE-ANGLE RELAYING SYSTEM 'FiledMay 10, 1944 o/ Relay,

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ATTORNEY Patented Oct. 8, 1946 CARRIER-CURRENT PHASE-ANGLE RELAYINGSYSTEM Arthur C. Mehring and Herbert W. Lensner, East Orange, andShirley L. Goldsborough, Basking Ridge, N. J., assignors to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania Application May 10, 1944, Serial No. 534,846'

23 Claims. 1

Our invention relates to improvements in pilotchannel relaying forprotecting transmission lines against faults, and it has particularrelation to that type of relaying in which a, carrier-current channel isutilized to produce a pulsating Waveform which is responsive to thephase of the linecurrent at a distant terminal or terminals of theprotected line.

Our invention is an improvement over the carrier-current relaying systemwhich is described and claimed in a Lensner application, Serial No.468,237, led December 8, 1942. The Lensner system utilized, at eachterminal, a saturated-current iine-current-responsive network forderiving a single-phase relaying voltage, of limited magnitude, from thepolyphase line-currents at that terminal, and for causing substantiallyflattopped or unmodulated carrier-current energy to be transmitted fromthat terminal on alternate half-cycles of the derived relaying voltage,so that, in the event of an internal fault, carrier would be transmittedon the same half-cycles of the line-current frequency, at both ends ofthe protected line-section, and the plate-current of the receiver tubewould consist of discrete, half-cycle impulses, which have a largealternating-current component which is utilized to pick up areceiverrelay, whereas an external fault causes the halfcycle periods ofcarrier-current transmission to alternate, at the opposite ends of theprotected line-section, so that the receiver plate-current issubstantially steady or constant in value, so that it has only a verysmall alternating-current component, which does not pick up thereceiver-relay.V

This original Lensner system, as just outlined, was a pioneer system ofits type, and it was quite workable, but i-t was subject to certaindifficulties, particularly in giving inconsistent operation, over a widerange of fault-currents, due to imperfections in the saturated-currentoperation, in being somewhat critical as to the tuning of thecarriercurrent receiver, and in being somewhat sensitive to the waveform, current-magnitude, or neon, lamp characteristics of thelimited-voltage network which derived the alternating-current relayingvoltage from the line-.current transformers.

' Our present invention is devised for the purpose of overcoming theseand other/difficulties, and for the purpose ofgreatly simplifying thecircuits and apparatus necessary for carrying out the general purpose ofthe Lensner invention.

A more particular object of our invention is to utilize receivedcarrier-current energy for the purpose of restraining the operation ofthe receiverrelay tube, or the tube which responds to receivedcarrier-current energy and which energizes the receiver-relay, insteadof utilizing the same to cause such operation. We provide a locallyenergized means for producing an operating voltage during half-cycles ofthe derived current-responsive voltage, the operating voltage beingopposite in sign from the restraining voltage, but of smaller magnitude,so that no plate-current is obtained in the receiver-relay tube if thehalf-cycle periods of carrier-current transmission at the remote end ofthe protected line-section coincide with the half-cycle impulses of thelocally derived operating voltage. In other words, we transmit carrieron derived line-current lhalf-cycles of one polarity, and We produce anoperating-voltage for the grid of the receiver-relay tube on halfcyclesof the opposite polarity, and we utilize the receipt of carrier-currentenergy to produce a restraining voltage, in the grid-circuit of thereceiver-relay tube.

A further object of our invention is to provide a trigger-circuitutilizing two gas triodes, or two grid-controlled gas tubes, havingtheir grid-circuits responsive to alternate potentials or halfcycles ofthe derived current-responsive relayingvoltage, so that each tube firesat an early portion of the line-current half-cycle to which it responds,the two tubes being interconnected together in such way that the firingof either tube extinguishes the other tube. With a steady direct-currentplate-voltage for energizing these two gas tubes, we are thus able toobtain alternate half-cycle periods of tube-operation, first one tubeoperating and then the other, in response to alternate half-cycles ofthe derived linecurrent, producing square-topped half-cycleplate-current waves which are steady in value and which are practicallyunaffected :by the line-current wave-form or magnitude, so that theapparatus is not critical in its response to the derived line-currento-r relaying-voltage.

A more specific object of our invention is to utilize these twotrigger-circuit gas triodes respectively for causing the intermittenttransmission of carrier, and for controlling the intermittent productionof the operating voltage for the grid of the relay-tube.

With the foregoing and other objects in View, our invention consists inthe circuits, systems, apparatus, combinations, parts, and methods,hereinafter described and claimed, and illustrated in the accompanyingdrawing, wherein:

Figure 1 is a diagrammatic View of circuits and apparatus illustratingan embodiment of our invention, and

Figs. 2 tc 13 are curve-diagrams which will be referred to in theexplanation of the invention.

In Fig. l, we show the terminal equipment for only one terminal of athree-phase transmission line I4, which is connected to a bus I5 througha three-phase circuit-breaker i5. Only one terminal equipment isillustrated, because the equipments at the other line-terminal orterminals are, or may be, identical to the illustrated equipment. Thecircuit-breaker i5 is illustrated as having a trip-coil TC, and anauxiliary make-contact breaker-switch la. The threephase line-current isderived by means of a bank of line-current transformers H, which respondto current-now into the protected line-section, at the terminal inquestion, and this three-phase line-current is fed into any suitablenetwork or filter, which is marked HCB, for deriving a singlephasealternating-current voltage at the network-terminals I3.

Any suitable network may be utilized for the network marked HCB, theidea being to derive a single-phase relaying quantity which isrepresentatively responsive to all different kinds of fault-currents.There are different networks for this purpose, a suitable one being thesocalled Type HCB network which is shown in the Harder patent,2,183,646, granted December 19, 1939, and assigned to WestinghouseElectric & Manufacturing Company. This HCB network is responsive to acombination of the positive-sequence and zero-sequence components of theline-cur` rent.

Usually and preferably, but not necessarily in accordance with ourpresent invention, the derived network-voltage is of limited magnitude,which may be accomplished by some saturating means such as a saturatingtransformer 25, the secondary terminals of which are shunted by avoltage-limiting glow-tube 2 l, as described in the Harder patent.

According to our invention, we provide two gas triodes or othergrid-controlled gas tubes GI and G2 of a sustained-discharge type; thatis, of a type in which the grid fires the tube, or starts the discharge,but is unable to extinguish the tube or interrupt the discharge. Thegrids of these tubes Gl and G2 are connected to the respective secondaryterminals 23 and 24 of the saturating transformer 20. An intermediatevoltage of the secondary transformer-circuit is derived from twoserially connected resistors Ri and R2, which are connected across thesecondary terminals 23 and 24. The connecting-point 25 between theseresistors is connected to a negative battery-terminal or bus through aC-battery Ec, which is so connected as to make the point 25 morenegative than the negative battery-terminal or, in general, so as tomake the point 25 have a, potential too negative, by a predeterminedamount, to cause the tubes GI and G2 to fire, under the impressedanodecathode voltage-conditions.

The cathode-circuits 26 and 27 of the gas tubes GI and G2 are connectedto the negative battery-terminal through cathode-resistors R3 and R4,respectively. The anode-circuits 2B and 30 of the respective gas tubesGI and G2 are respectively connected to plate-resistors R5 and R6, theother terminals of which are connected to a common conductor 3l which isconnected, through a make-contact 32 of a fault-detector FD, to thepositive battery-terminal (-1-). The fault-detector operating-coil, alsomarked FD, is energized from a secondary tap 33 of the satu- 4 ratingtransformer 20. The two anode-circuits 29 and 3B of the gas tubes Gl andG2 are joined by an interconnecting circuit containing a capacitor Cl.

The two gas tubes Gi and G2 are thus connected in a so-called triggercircuit, which operates as follows: During line-current halfcyoles ofone polarity, which we will call the negative half-cycles, or morespecifically during the negative half-cycles of the derivedcurrentresponsive voltage of the saturating transformer 2i), thesecondary terminal 23 is positive. At an early stage in these negativehalf-cycles, the positive voltage of the secondary terminal 23 withrespect to the secondary intermediate point 25, becomes more positivethan the blocking bias of the C-battery Ec, and the first gas tube GIres. It will be understood that the gas tubes have such characteristicsthat, when they are once fired, or when current is once started in theirplate-cathode circuits, such plate-cathode current will continue to flowuntil the voltage applied across the plate and cathode terminals of thetube is reduced to zero or reversed, even for a moment. At the beginningof the next-halfcycle of the output-voltage of the saturatingtransformer 20, which we call a positive halfcycle, the other secondaryterminal 24 becomes positive with respect to the secondary intermediatepoint 25, and fires the second gas tube G2.

Before the firing of the second tube G2, the potential of itsplate-circuit 30 was substantially the potential of the positivebattery-terminal assuming that the fault-detector contact 32 is closed,while the potential of the plate-circuit 29 of the first tube Gl was ata somewhat more negative value, due to the voltage-drop in theplate-resistor R5 of the first tube. When the second tube G2 res,however, its plate-circuit 3ll tends to drop to the same potential asthe plate-circuit 29 of the first tube, but the voltage-charge on theinterconnecting capacitor Cl causes the potential of the anode-circuit29 of the first tube Gi to momentarily drop to a value which is morenegative than the potential of the cathode circuit 26 of said first tubeGI, thus extinguishing the first tube GI in the moment required for thedischarge of the interconnecting capacitor Ci. In the next half-cycle,the first tube Gl fires again, and in turn extinguishes the second tubeG2 by momentarily causing a negative voltage to exist across itsplate-cathode terminals.

The function of the interconnecting capacitor which shunts off thepreviously firing gas tube when the second tube begins to fire, ispreferably supplemented by two capacitors C3 and C4, which are connectedin shunt across the respective cathode-resistors R3 and Re of the twogastubes Gl and G2. The effect of these shuntingcapacitors C3 and C4 isto short-circuit the associated cathode-resistor, R3 or R4, at the firstinstant of firing of the associated gas-tube, GI or G2, as the case maybe, thus momentarily bringing the anode-potential of the newly firedtube to a value which is more negative than the steady-stateanode-potential of the tube which was previously firing.

The interconnecting capacitor Ci, previous to the firing of the newlyfired tube, was charged in such polarity as to momentarily tend to holdthe anode-potential of the previously firing tube more negative than theanode-potential of the newly fired tube.

The combined effect of the three capacitors CI, C3 and C4 is to stronglydepress the anodepotential of the tube which was ring, at the firstinstant of ring of the second tube, making the anode-potential of thefirst tube momentarily more negative than its cathode-potential, thusextinguishing the tube. At the same time, the shunting-capacitor C3 orC4, as the case may be, of the tube that is being extinguished,momentarily holds up its cathode-potential to a value close to the valuewhich it had when the tube was firing, thus assisting in maintaining thereversed tube-voltage for the instant necessary to extinguish the tube.

According to our invention, we utilize the voltage-drops across the twocathode-resistors R3 and R4 to produce two diierent effects. Thevoltage-drop across the cathode-resistor R3 of the first gas tube GI isutilized to produce halfcycle impulses of square-topped positivevoltages for supplying a plate-voltage which is suicient for initiatingand maintaining the operation of an oscillator-tube OSC of acarrier-current transmitter, by connecting the plate-circuit 34 of theoscillator-tube OSC, through a radio-frequency choke RFC- L to thecathode-circuit 2B of the iirst gas tube GI, the cathode of theoscillator being connected, at 35, to the negative battery-terminal Thevoltage-drop across the cathode-resistor R4 of the second gas tube G2 isutilized to apply an operating voltage-ccmponent from thecathode-circuit 'd1 of the second tube G2 to the grid-circuit 36 of arelay-tube RT, which will be subsequently described. A voltage-dropresistor RIS is included in the connection between the cathode-circuit21 of the second trigger-tube G2 and the grid-circuit 35 of therelay-tube RT. y

Before further describing the carrier-current transmitter, we will referto other functions of the carrier-current equipment, which may beutilized during periods of no faul-ton the protected line-section I4. Wehave exempliiied these other or auxiliary carrier-current functions bymeans of a telemetering contact TM, which is utilized to control thetransmitter-oscillator OSC, either directly or indirectly. In theillustrated form of embodiment, the telemetering contact TM is utilizedindirectly to control the grid-circuit 31 of an auxiliary oscillatorOSC', which we call a keyer-oscillator. This keyer-oscillator OSC has acathode-circuit 38 which is connected directly to the negativebus-terminal and it has a plate-circuit 39 which is connected to thepositive bus (-1-) through a radio-frequency choke RFC- 2 and a resistorR1.

The cathode-circuit 38 of the keyer-oscillator OSC is also connected tothe mid-point between two capacitors C5 and C6, which cooperate with theprimary Winding of a transformer 4| toprovide a tunedoscillator-circuit, which is preferably, although not necessarily,tunedto a frequency which is higher than thatrof the maintransformer-oscillator OSC. The other terminal of the capacitor C5, thatis, the terminal opposite to the terminal 38, is connected to thegrid-circuit 31 of the keyer-oscillator OSC', while the other terminalof the capacitor C5 is connected, through a blocking capacitor BCI, tothe anodecircuit 39 of the keyer-oscillator OSC'. The keyer-oscillator'OSC' is also provided with a gridleak GLI, which is connected betweenthe gridcircuit 31and the cathode-circuit 38.

. The secondary circuit ot the transformer 4I of the keyer-oscillatorapparatus is utilized to energize a double-Wave rectifier-valve RV :solas to energize a, rectified-current loading-resistor R8 in vsuchpolarity as to provide a negative or blocking bias ona grid-controlcircuit 42. This gridcontrol circuit 42 is connected to the negative busthrough said loading-resistor R8 which is energized from therectifier-valve RV. The loading-resistance R8 is preferably shunted by aiiltercapacitor FCI, which smoothes out the ripples of theunidirectional voltage appearing across the terminals of the resistorR8.

The energization of the loading-resistor R8,

`through the rectifier-valve RV, from the keyeroscillator OSC', is suchthat a negative or blocking voltage is applied to the grid-circuitconductor 42 whenever the keyer-oscillator OSC is oscillating, but whenthe oscillations of the keyeroscillator OSC are blocked, thevoltage-drop through the loading-resistor R6 becomes negligible, so thatthe grid-circuit conductor 42 is substantially at the potential of thenegative batterysource (-l. y

The keyer-oscillator apparatus just mentioned is more particularlydescribed and claimed in a Lensner application Serial No. 530,134, ledApril 8, 1944. 1

The grid-circuit conductor 42 of the keyeroscillator apparatus isutilized for controlling the operation of the carrier-currenttransmitter which comprises the previously mentioned oscillator OSC, andtwo amplier-tubes AI and A2. The grid-control circuit 42 is connected tothe grid-circuit 43 of the transmitter-oscillator OSC through aradio-frequency impedance RFZ, and it is connected to the grid-circuits44 and v45 of the ampliiier-tubes AI and A2, by two voltagedividingresistors R9 and RIU, respectively.

In order that plate-voltage may be provided for thetransmitter-oscillator OSC during times when there is no 'fault on thetransmission-line I4, the circuit 26 may be connected to the positivebattery-terminal (-1-) through a back-contact 46 of the fault-detectorFD. In the illustrated embodiment of our invention, instead of beingdirectly connected to the positive terminal (-i-), the contact 46 isconnected to a tap-point41 near the positive end of a potentiometer RII-RI 2 which is connected across the direct-current terminals and Inoperation, the keyer-oscillator OSC normally oscillates, imposing ablocking bias on the grid-control circuit 42, so as to block theoperation of the transmitter-oscillator OSC. When the telemetering-keyTM is closed, however, the grid-leak GLI of the keyer-oscillator OSC' isshort-circuited, blocking the operation of said keyer-oscillator, andthus removing the blocking bias from the grids of thetransmitter-oscillator OSC and two amplifier-tubes AI and A2 of thecarrier-current transmitter, permitting the carrier-current transmitterto oscillate.

In order to prevent an unwanted blocking of the grid-control circuit 42at times when there is a fault on the transmission system, anotherfault-detector make-contact 48 is utilized, in shunt with thetelemetering-key TM, so that the closing of this fault-detector contactwill prevent the operation of the keyer-oscillator OSC when thetelemetering-key TM is open. Thus, the closing` of the fault-detectorcontact 48 removes the biasing voltage from the grid-control circuit 42.

The grid-circuit 43 of the transmitter-oscillator OSC is connected tothe cathode-circuit 35 of said oscillator through a grid-leak resistorGL2.

The anode-circuit 34 of the transmitter-oscillator OSC is coupled, bymeans of a blocking capacitor BCZ, to a conductor 49, which constitutesone junction-point of a tuned circuit which includes the conductor 49, acapacitor C6', the cathode-terminal 35, a capacitor C1, the gridterminal43, and a variometer VI, and thence back to the conductor 49. Theconductor 49 and the grid-terminal 43 are connected to the gridterminals44 and 45 of the amplifiers AI and A2 by means of blocking capacitorsBC3 and RC4, respectively.

The amplifier-tubes AI and A2 have a common cathode-circuit 50, which isconnected to the negative battery-terminal through a cathode-resistorRI3. The amplier-tubes AI and A2 have plate-circuits I and 52,respectively, which are connected to the primary-winding terminals of acoupling-transformer 53. The primary-winding mid-point 54 of thistransformer is connected to the positive battery-terminal (+L and it isalso connected, through a blocking capacitor BCE, to thecathode-terminal 50 of the amplifier-tubes.

One secondary-winding terminal of the coupling-transformer 53 isgrounded, at 51. Another tap-point 58 thereof is connected to avariometer s V2. and thence, through a coupling capacitor C-IIL to oneof the line-conductors of the protected line-section, in a manner whichis wellknown and needs no further description.

The secondary winding of the coupling-transformer 53 is provided withanother tap-point 68, which is connected to one terminal of the primarywinding of a receiver-coupling transformer G2, the other primary-windingterminal of which is connected, through a variable capacitor C-l I, tothe grounded point 51. The primary winding of the receiver-couplingtransformer 62 is also usually shunted by a voltage-limiting gas-tubeE4.

The receiver-coupling transformer 62 has a secondary winding, oneterminal of which is connected to the grid-circuit 65 of a detector-tubeor receiver-tube REC, while the other second-- ary-winding terminal isconnected to the negative battery-terminal The secondary winding of thereceiver-coupling transformer 62 is also shunted by a variable capacitorC-!2, in a manner which is usual in the art.

The receiver-tube REC is provided with a cathode-circuit 69 which isillustrated as being ccnnected to a tap-point 1n near the negative endof the potentiometer RI I-RI2. This tube also has an anode-circuit 1I,which is connected to the positive battery-terminal (-I-), through aradiofrequency choke RFC- 3 and the telemetering relays, which areindicated diagrammatically at 13.

In accordance with our invention, the plate or anode-circuit 1I of thereceiver-tube REC is also coupled, by means of a capacitor C-I3, to apoint 14 which is connected to the cathodecircuit 21 of the second tubeG2 through a large, capacitor-charging resistor RI4. The point 14 isalso connected, through a capacitor C-I, to a conductor which isconnected to the cathode-terminal 16 of the lower diode of a doublewaverectier-valve RV. The plate-circuit of this lower diode is connected tothe grid-terminal 38 of the relay-tube RT and to the voltagedrop orload-resistor RIS. The other terminal of the load-resistor RI5 isconnected to the cathode-circuit conductor 21 of the second gas triodeG2 as previously described. The upper diodecircuit 11 of the double-waverectifier-valve RV is connected, in the reverse polarity, between thecircuits 21 and 15. The load-resistor RIS is 8 shunted by aradio-frequency by-pass capacitor BPC.

The relay-tube RT is provided with a cathodecircuit which is connectedto an intermediate point of a potentiometer 8l, the terminals of whichare connected across the battery-terminals and (-I-). The relay-tube RTis also provided with a plate-circuit 82, which is connected to thepositive battery-terminal (-1-), through the primary winding of arelay-coupling transformer 84, the secondary of which is connected,through a rectifier-bridge 86, to the operating coil R of areceiver-relay R. The relay R is provided with a make-contact R, whichis shown near the top of Fig. 1, in series with the trip-coil TC of thecircuit-breaker I6. The output of the rectiiierbridge 86 may besmoothed, if desired, by means of a filter-capacitor FC2.

Our fault-detector FD is provided with a makecontact 88 which isconnected in the tripping circuit of the circuit-breaker I6, saidtripping circuit being traceable from the negative batteryterminalthrough the make-contact 88, and the receiver-relay contact R, to thetrip-coil TC. and thence through the breaker-switch 16a to the positivebattery terminal (-I).

The operation of the apparatus shown in Fig. 1 may best be explainedwith reference to the curvediagrams of Figs. 2 to 13. The lter HCB ofFig. 1, with its associated saturating transformer 20 andvoltage-limiting gas tube 2 I, produces an output-voltage, one part ofwhich appears across the conductors 24 and 25, and which is indicated,in Fig. 2, as a substantially sinusoidal single-phase wave which has anapproximately constant limiting magnitude, for all except the smallestof fault-currents, and which has a phase-angle which is determined by apredetermined function of the polyphase line-current at the relayingstation, said function ybeing determined by the characteristics of thelter, such as the diagrammatically illustrated filter marked HCB.

It is usually desirable to transmit carrier-current energy, forprotective relaying purposes, only during times of a fault somewhere onthe transmission system, and hence it is desirable to utilize some sortof fault-detector. In Fig. l, we have illustrated a fault-detector FD inthe form of an overvoltage relay which is energized from the saturatingtransformer 28, and which responds to the lightest faults to which aresponse is required. When this fault-detector responds, it picks up itsmake-contacts 32, 48 and 88, and it opens its back-contact 46. Themake-contact 32 applies the direct-current battery-voltage to theplate-cathode circuits of the two gas triodes GI and G2.

At a very early stage in each positive half-cycle of the filter-outputof Fig. 2, the second gas triode G2 lires, and produces a positivevoltage-impulse, which is obtained across the cathode-resistor R4, andcomprises the voltage from the negative battery-terminal to theconductor 21 in Fig. 1. We call this the operating voltage, as shown inFig. 3, because it is a voltage which tends to make the grid-terminal 36of the relaytube RT positive with respect to the cathode-circuit 80 ofthis tube, thus tending to cause current to flow in the plate-circuit 82of the tube. Since the gas triode G2 is energized from battery-terminalsand having a fixed voltage between them, and since the plate-cathodecircuits 30-21 of this triode are in series with fixed resistors R6 andR4, the positive voltage-impulses which make up the operating voltageare square- 9, topped,l and of a substantially constant magnitude, quiteirrespective of the magnitude of the 1ter-output or the wave-form of thelter-output. This is a considerable advantage, constituting a markedimprovement over anything that was previously utilized in this art.

At a very early period in each negative halicycle of the lter-outputwhich is shown in Fig. 2, the'rst gas triode Gl of Fig. 1 fires,immediately extinguishing the previously ring triode G2, in a mannerwhich has previously been described.. The operation of the rst gastriode Grl produces a succession of positive voltage-impulses whichalternate with the positive impulses which constitute the operatingvoltage of Fig, 3. The positive l voltage-impulses of the iirst triodeGl are obtained across the cathode-resistor R3, in the form of apositive voltage which appears between the negative battery-terminal andthe conductor 26, which is connected to the plate-circuit f 34 of thetransmitter-oscillator OSC', through the radio-frequency choke RFC- I ofFig. 1. rIhis causes the oscillator OSC to immediately beginoscillating, thus initiating the transmission of carrier. Thetransmission of carrier continues, at approximately its full, constantstrength, as long as the rst gas triode Gl is firing, which is to say,duringv the negative half-cycles of the lter-output of Fig. 2, as showndiagrammatically in Fig.4.

In Fig. 4, the frequency of the carrier-current Waves cannot be shown toscale, because the carrier-current frequency is actualy so high that itcould not begin to be shown in the space which we have allotted to Fig.4.

After the first impulse of carrier-current transmission, during the rstnegative half-cycle of the, filter-output after the response of thefaultdetector FD, the second gas'triode G2 again becomes conducting,extinguishing the first trlode Gl, and thus interrupting thecarrier-current transmission for a half-cycle period, corresponding tothe next positive half-cycle of the filteroutput.

It will be notedthat'the action just described occurs at both terminalsof the protected linesection I4, or at all of the terminals, in case theprotected line-section has more than two terminals. It will be notedthat the equipment at each terminal responds to the line-current inputinto I the protected line-section at its terminal, that is, from the busI5 at that terminal. In the event of an internal fault, that is, a faultwithin the connes of the protected line-section, the faultcurrent willbe flowing into the line-section at each terminal thereof, and thesefault-currents will be more or less in phase with each other, becausethe terminal-voltages of the line are not greatly out of phase with eachother, while the line-impedance which .limits the fault-current fromeach terminal to the fault-location has approximately the sameimpedance-angle in each case. For an internal fault, therefore, we mayassume, as a first approximation, that the faultcurrents are in phasewith each other at both or each of the line-terminals. 'I'his isdepicted in Fig. 5, which shows that the distant carrier, which istransmitted at another line-terminal other than the illustratedline-terminal, is transmitted vat the same time as the local carrierwhich is shown in Fig. 4, for an internal fault.

In the event of an external fault, however, current will be flowing outof the line-terminal which is closest to the external fault, and it willbe flowing into the protected line-section at at least onev otherterminal. Since each terminal equipment respondsv to a'current-direction looking into the protected line-section at thatterminal, the line-current at the terminal closest to the'external faultwill be reversed, approximately 180 in the ideal case, with respect tothe current in some other terminal. Hence, at each terminal, localcarrier will be transmitted at certain halfcycles of the line-frequency,as shown in Fig. 4, and distant carrier will be transmitted at somedistant terminal during line-frequency halfcycles which are displacedapproximately 180 (in the ideal case) with respect to the line-frequencyhalf-cycles of the local-carrier. Fig; 6 depicts the distantcarrier-current transmission for an external fault.

In the operation of the particular system shown in Fig. 1, it will benoted that carrier-current energy, from both the local and distanttransmitters, is-received by the receiver-tube REC, so as to produce aplate-cathode current through this tube during periods when thecarrier-current energy is being received. n

When no carrier-current energy is being received, the anode-terminal 1Iof the receivertube REC is practically at the potential of the positivebattery-terminal and hence the capacitor C|3 is charged in accordancewith the potential-,dierence between said anodeterminal 1| ofv thereceiver. and the cathode-terminal conductor 21 of the second gasYtriode G2, the receiver-connected terminal of the capacitor C-l3 beingpositive.` The conductor 21 has a potential such as is' depicted in Fig.3, varying between zero, which is taken as the potential of the negativebattery-terminal-V and a fraction of the total battery-voltage, which isutilized as the operating-voltage for the grid-circuit 36 of therelay-tube RT,this operating-voltage` being the Voltage-drop of thecathode-resistor R4 of-the second gas triode G2, whenever the latter isfiring. Y

. When carrier-current energy is received, the receiver-tube REC becomesconducting, Pulling down the potential of its anode-terminal 1l -to apoint which is more or less close to the potential of the negativebattery-terminal thus more or less short-circuiting the capacitor C l3,and causing it to discharge, drawing'current through the load-resistorR15 and the lowerdiode of the rectier-valve RV', said diode beingconnected in such polarity as to permit currentflow in the directionAfrom theconductor 21 to the conductor 36, and thence through the lowerdiode to the conductor 16and the capacitors C-I4 and (1 -I3. At the sametime, a much smaller curren-t flows through the much largercapacitor-charging resistance RH, which is utilized to charge thecapacitor C-I3. l

During the periods when no carrier-current energy is being received, inthe illustrated form of embodiment of our invention, the receiverplate-circuit 1| again becomes quite positive, so that the upperdiode-circuit 11 of the rectiervalve RV becomes conducting and chargesthe capacitor C-I4, making the terminal 14 positive and the terminal 15`negative, thus causing the capacitorC-M to act as a voltage-doubler fordoubling the effective voltage of the capacitor C`-I3. Y

When, therefore, carrier-currentl energy is again received, on the nexthalf-cycle of the linefrequency current, the two capacitors `C--M andC-l3 discharge through the load resistor-RIS, thus producing a negativeor restraining voltagedrop in the load resistor RIS, making theconductor 36, and hence the grid of the relay-tube RT, negative withrespect to the potential of the cathode-circuit conductor 21 of thesecond gas tube G2. The reception of carrier-current thus causes thecapacitors C-I4 and C-I3 to discharge, producing a voltage-drop in theloadresistor RIS, making the grid of the relay-tube RT more negative,and thus eilectually preventing this tube from operating in response tothe operating-voltage which is produced by the current-flow in thecathode-resistor R4 of the second gas tube G2.

The radio-frequency or carrier-frequency component of the plate-voltageof the receiver-tube REC is by-passed from the load-resistor RIS by theby-passing capacitor BPC.

Fig. 7 shows the negative or restraining voltage, across the resistorR|5, for an internal fault in which the fault-currents are in phase witheach other at both or all of the line-terminals, while Fig. 8 shows thecorresponding restraining voltage for an external fault in which theoutwardly flowing current at one line-terminal is exactly 180 out ofphase with the inwardly ilowing current or currents at the otherterminal or terminals of the protected line-section.

The receiver-tube REC preferably has a constant-current characteristic,so that Whenever its grid permits plate-current to now, the platecurrentwill have an approximately constant value. Thus, as shown in Fig. 8, thehalf-cycles of receiver plate-current, during which carriercurrentenergy is being received by the receivertube REC from the distantcarrier, transmitted from some other line-terminal, are of anapproximately fixed magnitude, regardless of carriercurrent attenuation.Hence the restraining voltage-impulses in the resistor RIS are of anapproximately xed magnitude. The receiver plate-current impulses whichare received from the distant carrier are of approximately the samemagnitude as the half-cycle impulses of platecurrent which are producedwhen carrier-current energy is being received from the localtransmitter, even though the local signals may be the stronger.

It is preferable, also, that the relay-tube RT shall have aconstant-current characteristic, so that its plate-current shall beconstan-t, as shown in Fig. 11, without sensitive dependence upon theprecise magnitude of its grid-voltage. Thus, the exact amount of therestraining voltage, produced by the receipt of carrier-current energy,as shown in Fig. 8, is not important, so long as said restrainingvoltage is greater than the operating voltage of Fig. 3, or thevoltage-drop in the resistor R4, by a safe margin.

It is further to be noted that the only carriercurrent response of anymoment is the response to the distant carrier, that is, thecarrier-current impulses which are transmitted from some otherline-terminal or terminals. 'I'he carrier-current energy received fromthe local carrier-current transmitter is immaterial, because, by thevery nature of the control, it is always transmitted (and received)during the half-cycles alternating between the half-cycles when theoperating impulses of Fig. 3 are present.

The grid-voltage of the relay-tube RT is thus made up of threecomponents: First, there is a negative grid-bias consisting of thevoltage between the potentiometer-tap 80 and the negativebattery-terminal, which is suflicient to bias the grid of the relay-tubeRT so that no plate-current flows in said tube When there is norestraining or operating Voltage present. A second component of thegrid-voltage of the relay-tube RT is the operating voltage, in the formof positive voltageimpulses produced Whenever the cathode-circuitcurrent of the second gas tube G2 flows through the cathode-resistor R4,as shown in Fig, 3. The third grid-voltage component of the relay-tubeRT is the restraining voltage, in the form oi.' negativevoltage-impulses as shown in Figs. 7 and 8, for an internal fault and anexternal fault, respectively. This restraining voltage is produced bythe discharge of the capacitors C`|4 and C--l3 through the resistor RIEwhenever carrier-current energy is being received from anyline-terminal, although the restraining impulses which are received froma distant line-terminal are the only ones of importance. The resultantgrid-voltage of the relay-tube RT is shown in Figs. 9 and 10, for aninternal fault and an eidternal fault, respectively.

Since the relay-tube RT will be operated, or carry a plate-current, onlywhen its grid is sufiiciently positive with respect to its cathode, aplate-current will ow in the relay-tube RT only during the positivehalf-cycles of the grid-voltages shown in Figs. 9 and 10, that is, onlywhen the local operating impulses of the second-valve cathode-circuitconductor 21 and its cathoderesistor R4 are not opposed by therestraining impulses received from a distant line-terminal.

When there is an internal fault, accompanied by fault-currents which arein phase with each other at the several line-terminals, the platecurrentof the relay-tube RT takes the form of a succession of square-toppedhalf-cycles corresponding in timing to the line-frequency halfcycleswhen the second gas tube G2 is firing, as depicted in Fig. 11, thusenergizing the local tripping-relay R and causing a localtripping-operation.

In the case of an external fault, with line-currents exactly c out ofphase with each other, the grid-biasing voltage of the relay-tube RT isentirely negative, as shown in Fig. 10, and the plate-current of therelay-tube RT is zero, as shown in Fig. 12, meaning no response of therelay R, and hence no tripping-operation.

While We have discussed the ideal cases of an internal fault in whichthere is a 0 phase-angle between the terminal line-currents, and anexternal fault in which there is a 180 phase-displacement, countinginwardly ilowing currents as positive, or in phase with each other, ateach terminal, it is to be noted that, in actual cases, the terminalline-currents for internal faults will not, in general, be exactly inphase with each other, but will vary in phase, by a certain amount, sothat the impulses of the plate-current of the relay-tube will beshorter'than the half-cycle impulses shown in Fig. 11, depending uponthe phase-angle, because the operating impulses of Fig. 3 will bepartially overlapped or blocked by received impulses from the distanttransmitter, according to the phase-angle between the faultcurrents atthe different stations.

Fig. 13 shows a plot of the integrated, or rootmean-square, or averaged,current in the relaycoil R, in milliamperes, plotted against thephaseangle of the terminal line-currents. It shows that, as thephase-angle departs from zero, in either the leading direction or thelagging direction, the relay-current falls oil?, or becomes smaller andsmaller, until the phase-angle becomes 180. The receiver-relay R isreally an overcur- 13 rent relay, and lit is adjusted to have a pick-upvalue 99 (Fig. 13) which permits the internalfault currents at theseveral terminals to be out of phase with each other as much as 120,while still permitting the fault-responsive receiverrelay R to pick up.This leaves the phase-angles between 120 and 180 to represent,external-fault conditions, during which the relay R does not pick up. Itwill be understood, of course, that the pick-up value of therelay-current can be set `for any desired magnitude, corresponding toany desired phase-angle between the terminal linecurrents, in accordancewith the necessities of special conditions existing on any particularline. y The relay-tube RT preferably has a constantcurrentcharacteristic, so that whenever its grid permits plate-current to flow,the plate-current willvhave an approximately constant value, as shown inFig. 11, without sensitive dependence upon the precise magnitude of thegrid-voltage. Hence, the integrated, or root-mean-square, or average,value of the plate-current will depend only upon the relative lengths ofthe time-periods during which the plate-current is flowing, as shown inFig. 13.

Since the relay-current is measured in milliamperes, it is usually moreconvenient to utilize a sensitive polarized relay R, or other sensitivedirect-current relay R, to respond to this platecurrent, rather thanutilizing an alternatingcurrent relay for this purpose. For this reason,we have provided the plate-circuit transformer 84, and therectifier-bridge 85, so that we may utilize a sensitive direct-currentmilliampere-relay R, as shown in Fig. 1.

The relay R, as previously described, has a make-contact in thetripping-circuit of the breaker I6, so that, whenever the relay R picksup, the circuit-breaker I6 is tripped. lBecause of the sensitive natureof the relay R, and the possibility of shock-excitation of thecarrier-current receiver-circuits due to static conditions, or the like,it is usually desirable to safeguard the tripping-circuit by providingsome additional faultresponsive contact, in addition to the contact ofthe relay R, and we have provided for this, in Fig. 1, by means of thecontact 88 oi the faultvdetector FD, which is intended to berepresentative of any fault-detector contact which is controlledindependently of the carrier-current channel, and which is intendedmerely to make sure that there is a fault somewhere on the transmissionsystem, before a tripping operation is permitted in response to thereceiver-relay contact R. During fault-free conditions, when there is nofault on the transmission system, it is usually desirable to make use ofthe carrier-current channel for purposes other than protective relaying.We have illustrated such purposes in the form of the telemetering-keyTM. When there is no fault on the transmission system, thefault-detector FD'is unresponsive. The fault-detector contact 32, in theenergizing-circuit of the two gas triodes Gl and G2, prevents theproduction of any voltage-drops across the cathode-resistors R3 and R4of these gas triodes. The drop across theresistor R3 prevents theproduction of any triode-responsive plate-voltage for causingcarriet-current transmission as a result of the operation of thetransmitter-oscillator OSC. The drop across the resistor R4 prevents theproduction of any operating voltage on the grid of the relay-tube RT.

In order to provide an energizing-'circuit for thetransmitter-oscillator OSC, which is available during no-fault periodsoi the normal transmission-line operation, we provide the fault-detectorcontact 4B, which Connects the circuit 26 to the positivebattery-terminal under these conditions. At the same time, however, thatis, when there is no fault on the transmission system, the faul-detectorcontact 48 is open, so that the normally open position of thetelemetering-key TM makes it possible for the keyer-oscillator OSC tooscillate, thus developing a biasing voltage-drop in the load-resistorR8, and blocking the operation of both the transmitter-oscillator OSCand its associated amplifier-tubes Al and A2, during these conditions,which may be regarded as corresponding to the normal conditions whenthere is no fault on the transmission system. l

When it is desired to utilize the carrier-current channel duringfault-free conditions, carrier-current transmission is started, andcontrolled or modulated, in any desired manner, according to the usewhich is to be made of the channel. For telemeterng uses, thetelemeteringkey TM is rapidly closed and opened, at a certain rate, oraccording to a predetermined code, thus causing carrier to betransmitted during the moments when the key TM is closed, and operatingthe telemetering relay 13, at both ends of the protected line-section,in accordance with the manipulation of the telemetering-key TM.

Since our illustrated system utilizes only one fault-detector, which isshown at=FD, it is necessary Vto guard against erroneous relay-operationin the event of a distant fault which might cause a picking up of thefault-detector at only one end of the protected line-section. Toeliminate the possibility of incorrect relaying under these conditions,we prefer to arrange the circuit constants so that the gas triode GIwhich controls carrier res at a lower voltage of the lter output-circuit23-24 than the gas triode G2 which provides operating voltage to thegrid-circuit 38 of the relay-tube RT.

The gas triode Gl which controls carrier fires at about the same timethat the fault-detector FD picks up, preferably immediately upon theattainment of a voltage which will cause the detector FD to pick up. Thesecond gas triode G2 res at a grid-voltage which is sufliciently abovethe pick-up voltage of the detector FD to insure that thefault-detectors FD at both ends of the line-section will pick up beforethe second gas triode G2 applies an operating voltage to the relay-tubeRT at either end of the line. Consequently, if only one fault-detectorpicks up, at only one end of the line, there will not be enoughcontrol-voltage across 23 and 24 to cause the diode G2 to fire at eitherend of the line, and hence the relay-tube RT cannot carry current tooperate the receiver-relay R at either end of the line.

In Fig. 1, the resistor R2 is illustrated as being larger than RI, sothat, with identical tubes GI and G2, the tube GI will receive thelarger portion of the voltage across 23 and 24. The tube G2 may fire ata voltage which is 20% to 50% above the control-voltage (across 23 and24) which results in the firing of the tube GI.

While we have illustrated our invention in but a single form ofembodiment, which we at present prefer, we desire it to be understoodthat such illustration is only illustrative, and that various changes ofomission and. addition and substitution may be made without departingfrom many of the essential features of our invention, as will be Wellunderstood by those skilled in the art. We desire, therefore, that theappended claims shall be accorded the broadest construction consistentWith their language.

We claim as our invention:

l. Terminal equipment for one terminal of a pilot-channel phase-anglerelaying system for an alternating-current transmission-line, comprisingline-current-responsive means for deriving a succession of substantiallyflat-topped operating impulses at times during positive line-currenthalf-cycles, line-current-responsive pilotchannel means for transmittinga succession of restraining impulses to another line-terminal orterminals at times during negative line-current half-cycles of theline-current at the relaying terminal at which said terminal equipmentis located, and relay-means for developing a variable operating forceonly during those portions of the operating impulses during which norestraining impulses are being received from a distant lineterminal.

2. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means, operative during conditions of fault onthe transmission system, for deriving a succession of substantiallyconstantmagnitude operating-impulses, each of substantially half-cycleduration, in response to successive line-current half-cycles of onepolarity, at the relaying terminal; line-current-responsivepilot-channel means, operative during conditions of fault on thetransmission system, for transmitting a succession of substantiallyconstant-magnitude restraining-impulses, each of substantiallyhalf-cycle duration, to another line-terminal or terminals in responseto successive linecurrent half-cycles of the opposite polarity, at therelaying terminal; and relay-means for developing a relay-operatingforce of variable magnitude dependent upon the proportion of the timeduring which the half-cycle operating-impulses are not being blocked byrestraining-impulses which are received from a distant line-terminal.

3. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means for deriving a succession of substantiallyflat-topped operating impulses at times during positive line-currenthalf-cycles, line-current-responsive pilot-channel means fortransmitting a succession of restraining impulses to anotherline-terminal or terminals at times during negative line-currenthalf-cycles of the line-current at the relaying terminal at which saidterminal equipment is located, means for developing a relaying currentonly during those portions of the operating impulses during which norestraining impulses are being received from a distant line-terminal,and relay-means responsive to a predetermined integrated value of saidrelaying current.

4. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means, operative during conditions of fault onthe transmission system, for deriving a succession of substantiallyconstantmagnitude operating-impulses, each of substantially half-cycleduration, in response to successive line-current half-cycles of onepolarity, at the relaying terminal; line-current-responsivepilot-channel means, operative during conditions of fault on thetransmission system, for transons mitting a succession of substantiallyconstantmagnitude restraining-impulses, each of substantially half-cycleduration, to another line-terminal or terminals in response tosuccessive linecurrent half-cycles of the opposite polarity, at therelaying terminal; means for developing a relaying current of relativelynXed magnitude during times during which the half-cycleoperating-impulses are not being blocked by restraining-impulses whichare received from a distant line-terminal, and relay-means responsive toa. predetermined integrated value of said relaying current.

5. Terminal equipment for one terminal of a pilot-channel phase-anglerelaying system for an alternating-current transmission-line, comprisingline-current-responsive means for deriving a succession of substantiallyflat-topped operating impulses at times during positive line-currenthalfcycles, line-current responsive pilot-channel means for transmittinga succession of restraining impulses to another line-terminal orterminals at times during negative line-current halfcycles of theline-current at the relaying terminal at which said terminal equipmentis located, a relay-tube having control-circuit means, means forutilizing said operating impulses and said restraining impulses in saidcontrol-circuit means, and relay-means responsive to a predeterminedintegrated value of plate-cathode current in said relay-tube.

6. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means, operative during conditions of fault onthe transmission system, for derivinga succession of substantiallyconstantmagnitude operating-impulses, each of substantially half-cycleduration, in response to successive line-current half-cycles of onepolarity, at the relaying terminal; line-current-responsivepilot-channel means, operative during conditions of fault on thetransmission system, for transmitting a succession of substantiallyconstant-magnitude restraining-impulses, each of substantiallyhalf-cycle duration, to another line terminal or terminals in responseto successive line-current half-cycles of the opposite polarity, at therelaying terminal; a relay-tube having control-circuit means normallyadjusted s0 that substantially no plate-cathode current flows in saidtube; means for impressing said operatingimpulses and saidrestraining-impulses on said control-circuit means; and relay-meansresponsive to said plate-cathode current.

7. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprising line-currentresponsive means for deriving a relaying quantity of limited magnitudefor responding to the phase-angle of the line-current input into thetransmission-line at that terminal, pilot-channel means for transmittinga relaying quantity of limited magnitude to another line-terminal orterminals for responding to the phase of the relaying quantity at thetransmitting terminal, circuit-means for combining the relaying quantityderived at the relaying terminal and the relaying quantity received froma distant line-terminal or terminals in such manner as to discriminateas to the phase-angular relations of said relaying quantities` arelay-tube having a control-circuit responsive to said circuit-means.and relaymeans responsive to the plate-cathode current in saidrelay-tube.

8. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprising line-currentresponsive means for deriving an alternating-current relaying quantityat the relaying terminal, two gas tubes of the sustained-discharge type,each tube having trigger-acting controlcircuit means for firing thetube, direct-current plate cathode circuit energization means for saidtwo gas tubes, interconnecting impulsingmeans between the plate-cathodecircuits of said two gas tubes .for responding to the moment of firingof either tube in such manner as to so impulse the effectiveplate-cathode voltage across the other tube as to extinguish said othertube, means for so applying said relaying quantity to thecontrol-circuit means of the two gas tubes that the tubes re duringhalf-cycles of opposite polarity of said relaying quantity, and meansincluding pilot-channel means for utilizing the intermittent operationof at least one of said two gas tubes for obtaining a response to therelative phase-angles of the relaying 'quantities derived at a pluralityof different line-terminals.

9. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means, operative during conditions of fault onthe transmission system, for deriving an alternating-current relayingquantity at the relaying terminal, two gas tubes of thesustained-discharge type, each tube having triggeracting control-circuitmeans for firing the tube, direct-current plate cathode circuitenergizetion-means for said two gas tubes, interconnectingimpulsing-means between the plate-cathode circuits of said two gas tubesfor responding to the moment of iii-ing of either tube in such manner asto so impulse the eiective plate-cathode voltage across the other tubeas to extinguish said other tube, means for so applying said relayingquantity to the control-circuit means of the two gas tubes that thetubes nre during halfcycles of opposite polarity of said relayingquantity, means for obtaining a succession of operating-voltage impulsesin response to the intermittent operation ofA one of said two gas tubes,means including pilot-channel means for responding to the intermittentoperation of the other gas tube for transmitting a succession ofrestraining-voltage impulses to another line-terminal or terminals, andrelay-means for developing a relay-operating force of variable magnitudedependent upon the proportion of the time during which the half-cycleoperating-impulses are not being blocked by restraining-impulses Vwhichare received from a distant line-terminal.

10. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means for deriving a succession:

of substantially nat-topped operating impulses at times during positiveline-current half-cycles, line-current-responsive carriercurrent meansfor transmitting a succession of restraining impulses to the.transmission-line at times during negative line-current half-cycles ofthe line-current at the relaying terminal at which said terminalequipment is located, and relay-means for developinga variable operatingforce only during those portions of the operating impulses during whichno restraining impulses are being received from the carrier-current onthe transmission-line.

l1. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means, operative during conditions of fault onthe transmission system, for deriving a succession of substantiallyconstantmagnitude operating-impulses, each of substantially half-cycleduration, in response to succesvsive line-current half-cycles, of onepolarity, at

the relaying terminal; line-current-responsive carrier-current means,operative during conditions of fault on the transmission system, fortransmitting a succession of substantially constarrt-magnituderestraining-impulses, each of substantially half-cycle duration, to thetransmission-line in response to successive line-current half-cycles ofthe opposite polarity, at the relaying terminal; and relay-means fordeveloping a relay-operating force of variable magnitude dependent uponthe proportion of the time during which the half-cycleoperating-impulses are not being blocked by restraining-impulses whichare received from the carrier-current on the transmission-line.

12. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means for deriving a succession of substantiallyflat-topped operating impulses at times during positive line-currenthalf-cycles, line-current-responsive carrier-current means fortransmitting a succession of restraining impulses to thetransmission-line at times during negative line-current half-cycles ofthe line-current at the relaying terminal at which said terminalequipment is located, means for developing a relaying current onlyduring those portions of the operating impulses during which norestraining impulses are being received from the carrier-current on thetransmission-line, and relay-means responsive to a predeterminedintegrated value current transmission-line, comprisingline-current-responsive means, operative during conditions of fault onthe transmission system, for deriving a succession of substantiallyconstantmagnitude operating-impulses, each of substantially half-cycleduration, in response to successive line-current half-cycles,of onepolarity, at the relaying terminal; line-current-responsivecarrier-current means, operative during conditions of fault on thetransmission system, for transmitting a succession of substantiallyconstant-magnitude restraining-impulses, each of substantiallyhalf-cycle duration, to the transmission-line in response to successiveline-current half-cycles of the opposite polarity, at the relayingterminal; means for developing a relaying current of relatively fixedmagnitude during times during which the half-cycle operating-impulsesare not being blocked by restraining-impulses which are received fromthe carrier-current on the transmission-line, and relay-means responsiveto a predetermined integratedvalue of said relaying current.

14. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means for deriving a succession of substantiallyflat-topped operating impulses at times during positive line-currenthalf-cycles, line-current-responsive means for transmittingcarrier-current signals to the transmission-line at times duringnegative line-current half-cycles of the line-current at the relayingterminal at which said terminal equipment is located, carrier-.currentreceiver-means for obtaining a succession of restraining impulses attimes when there are carrier-current signals on the transmission-line, arelay-tube having control-circuit means, means for utilizing saidoperating impulses and said restraining impulses in said control-circuitmeans, and relay-means responsive to a predetermined integrated value ofplate-cathode current in said relay-tube.

15. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprising line-currentresponsive means, operative during conditions of fault on thetransmission system, for deriving a succession of substantiallyconstant-magnitude operating-impulses, each of substantially half-cycleduration, in response to successive linecurrent half-cycles of onepolarity, at the relaying terminal; line-current-responsive means,operative during conditions of fault on the transmission system, fortransmitting a succession of substantially constant-magnitudecarrier-current signals, each of substantially half-cycle duration, tothe transmissionrline, in response to successive line-currenthalf-cycles of the opposite polarity, at the relaying terminal;carrier-current receiver-means for obtaining a succession of restrainingimpulses at times when there are carrier-current signals on thetransmission-line; a relay-tube having control-circuit means normallyadjusted so that substantially no plate-cathode current flows in saidtube; means for impressing said operating-impulses and saidrestraining-impulses on said control-circuit means; and relaymeansresponsive t said plate-cathode current.

15. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprisingline-current-responsive means, operative during conditions of fault onthe transmission system, for deriving an alternating-current relayingquantity at the relaying terminal, two gas tubes of thesustained-discharge type, each tube having triggeracting control-circuitmeans for iiring the tube, direct-current plate-cathode-circuitenergia-.ationmeans for said two gas tubes, interconnectingimpulsing-means between the plate-cathode circuits cf said two gas tubesfor responding to the moment of ring of either tube in such manner as toso impulse the effective plate-cathode voltage across the other tube asto extinguish said other tube, means for so applying said relayingquantity to the control-circuit means of the two gas tubes that thetubes rire during half-cycles of opposite polarity of said relayingquantity, means for obtaining a succession of operating voltage impulsesin response to the intermittent operation of one of said two gas tubes,means responsive to the intermittent operation of the other gas tube fortransmitting a succession of restraining-voltages to the transmissionline, and relay-means for developing a relay-operating force of variablemagnitude dependent upon the proportion ol the time during which thehalfcycle operating-impulses are not being blocked by restrainingimpulses which are received from a distant line-terminal.

17. Carrier-current control-means for a protective relaying system foran alternating-current transmission-line, including, at each of aplurality of line-terminals, line-current-responsive means for derivingan alternating-current relaying quantity at the relaying terminal, twogas tubes of the sustained-discharge type, each tube havingtrigger-acting control-circuit means for firing the turbe,direct-current plate-cathodecircuit energization-means for said two gastubes, interconnecting impulsing-means between the plate-cathodecircuits of said twc gas tubes for responding to the moment of firing ofeither tube in such manner as to so impulse the effective plate-cathodevoltage across the other tube as to extinguish said other tube, meansfor so applying said relaying quantity to the control-circuit means ofthe 'vo gas tubes that the tubes fire during haii-cycles of oppositepolarity of said relaying quantity, carrier-current relaying equipmentincluding a carrier-current transmitter having a tube, and means forutilizing the intermittent operation of at least one of said two gastubes for intermittently energizing the platecathode circuit of saidtube of the carrier-current transmitter.

13. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprising localcontrol-means, responsive solely to the local linecurrent, for derivinga succession of operating impulses at all times of fault during positivelinecurrent hall-cycles, line-current-responsive pilotchannel means,responsive solely to said local conrol-means, lor transmitting asuccession of restraining impulses and making them eiective at anotherline-terminal or terminals at all times oi fault during negativeline-current half-cycles of the line-current at the relaying terminal atwhich said terminal equipment is located, and relay-means responsivesolely to said operating impulses and said restraining impulses fordeveloping a variable operating force only during those portions of theoperating impulses during which no restraining impulses are beingreceived from a distant line-terminal.

19. Terminal equipment for a pilot-channel phase-angie relaying systemfor an alternatingcurrent transmission-line, comprising localcontrol-means, responsive solely to the local line-current, for derivinga succession of operating impulses at all times of fault during positivelinecurrent haii-cycles, line-current-responsive pilotchannel means,responsive solely to said local control-means, for transmitting asuccession of restraining impulses and making them effective at anotherline-terminal or terminals at all times of fault during negativeline-current half-cycles of the line-current at the relaying terminal atwhich said terminal equipment is located, means responsive solely tosaid operating impulses and said restraining impulses for developing arelaying current only during those portions of the operating impulsesduring which no restraining impulses are being received from a distantlineterminal, and relay-means responsive to a predetermined integratedvalue of said relaying current.

20. Terminal equipment for a pilot-channel phase-angle relaying systemfor an alternatingcurrent transmission-line, comprising localcontrol-means, responsive solely to the local linecurrent, for derivinga succession of operating impulses at all times of fault during positivelinecurrent half-cycles, line-current-responsive pilot-channel means,responsive solely to said local control-means, for transmitting asuccession of restraining impulses and making them effective at anotherline-terminal or terminals at all times oi fault during negativeline-current half-cycles of the line-current at the relaying terminal atwhich said terminal equipment is located, a relaytube havingcontrol-circuit means, means'for utilizing only said operating impulsesand said restraining impulses in said control-circuit means, andrelay-means responsive to a predetermined integrated value ofplate-cathode current in said relay-tube.

21. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprising localcontrol-means, responsive solely to the local line-current, for derivinga succession of operating irnpulses at all times of fault duringpositive linecurrent half-cycles, line-current-responsivecarrier-current means, responsive solely to said local control-means,for transmitting a succession of restraining impulses and making themeffective at one or more terminals of the transmission-line at all timesof fault during negative line-current half -cycles of the line-currentat the relaying terminal at which said terminal equipment is located,and relay-means responsive solely to said operating impulses and saidrestraining impulses for developing a variable operating force onlyduring those portionsof the operating impulses during which norestraining impulses are being received from the carrier-current.

22. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprising localcontrol-means, responsive solely to the local linecurrent, for derivinga succession of operating imv pulses at all times of fault duringpositive linecurrent half-cycles, line-current-responsivecarrier-current means, responsive solely to said local control-means,for transmitting a succession of restraining impulses and making themeffective at one or more terminals of the transmission-line at all timesof fault during negative line-current half-cycles of the line-current atthe relaying terminal at which said terminal equipment is located, meansresponsive solely to said operating impulses and said restrainingimpulses for developing a relaying current only during those portions ofthe operating impulses during which no restraining impulses are beingreceived from the carrier-current, and relay-means responsive to apredetermined integrated value of said relaying current.

23. Terminal equipment for a carrier-current phase-angle relaying systemfor an alternatingcurrent transmission-line, comprising localcontrol-means, responsive solely to the local linecurrent, for derivinga succession of operating impulses at all times oi fault during positivelinecurrent half cycles, line current responsive means, responsivesolely to the local controlmeans, for transmitting carrier-currentsignals to the transmission-line at all times of fault during negativeline-current half-cycles of the linecurrent at the relaying terminal atwhich said terminal equipment is located, carrier-current receiver-meansfor obtaining a succession of restraining impulses at times when thereare carrier-currentv signals on the transmission-line, a relay-tubehaving control-circuit means, means for utilizing solely said operatingimpulses and said restraining impulses in said control-circuit means,and relay-means responsive to a predetermined integrated value ofplate-cathode current in said relay-tube.

ARTHUR C. MEHRING. HERBERT W. LENSNER. SHIRLEY L. GOLDSBOROU GH.

